chore: remove obsolete buster-backports apt source from builder stages

[crenshaw-dev]

Summary

Remove the stale buster-backports apt source from the golang builder stages in Dockerfile and Dockerfile.tilt.

This repo line was originally added in #1941 (July 2019) to install git-lfs from Debian backports on the golang/Debian-based builder image. At the time, git-lfs was not available in Debian Stretch/Buster main repos.

Since then:

• 2021 (chore: Switch Docker base image to ubuntu:20.10 instead of debian:10-slim #5185): argocd-base switched to Ubuntu and dropped the backports line (Ubuntu had git-lfs in its own repos), but it was left on the builder stage because that stage still uses the golang/Debian image.
• 2024 (fix: docker build fails due to 'http://deb.debian.org/debian buster-backports Release' does not have a Release file. #17836): The URL was changed from deb.debian.org to archive.debian.org after active Debian mirrors dropped buster-backports.
• 2026 (chore: install git-lfs 3.7.1 version using an install script #26465): git-lfs was removed from apt install and is now installed via install.sh, but the backports line was not cleaned up.

The golang image is now Debian Trixie (13), and all remaining builder packages (nginx, fcgiwrap, openssh-server, etc.) are available in main repos without backports. The Ubuntu base image stages are unaffected — they use the built-in resolute sources from ubuntu:26.04.

There is no indication git-lfs will move back to apt: #26465 moved it to install.sh because upstream stopped publishing Debian packages as of 3.7.0, and the project now pins the version in hack/tool-versions.sh like helm and kustomize.

Test plan

• Verified docker build --target builder succeeds without the backports line

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this does not need to be in the release notes.
• The title of the PR states what changed and the related issues number (used for the release note).
• The title of the PR conforms to the Title of the PR
• I've included "Closes [ISSUE #]" or "Fixes [ISSUE #]" in the description to automatically close the associated issue.
• I've updated both the CLI and UI to expose my feature, or I plan to submit a second PR with them.
• Does this PR require documentation updates?
• I've updated documentation as required by this PR.
• I have signed off all my commits as required by DCO
• I have written unit and/or e2e tests for my change. PRs without these are unlikely to be merged.
• My build is green (troubleshooting builds).
• My new feature complies with the feature status guidelines.
• I have added a brief description of why this PR is necessary and/or what this PR solves.
• Optional. My organization is added to USERS.md.
• Optional. For bug fixes, I've indicated what older releases this fix should be cherry-picked into (this may or may not happen depending on risk/complexity).

Made with Cursor

[bunnyshell]

❗ Preview Environment deployment failed on Bunnyshell

See: Environment Details | Pipeline Logs

Available commands (reply to this comment):

• 🚀 /bns:deploy to redeploy the environment
• ❌ /bns:delete to remove the environment

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (master@08e959d). Learn more about missing BASE report.
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master   #28250   +/-   ##
=========================================
  Coverage          ?   64.75%           
=========================================
  Files             ?      424           
  Lines             ?    58714           
  Branches          ?        0           
=========================================
  Hits              ?    38021           
  Misses            ?    17161           
  Partials          ?     3532           

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.